Xerographic printing and reproduction machines, such as that shown schematically in FIG. 1, typically include raster scanners: raster output scanners (ROSs) for printing and raster input scanners (RISs) for image acquisition in reproduction. In raster scanning systems, an imaging light beam scans across a rotating polygon to a movable photoconductive member, recording or writing electrostatic latent images on the member. Generally, a ROS has a laser for generating a collimated beam of monochromatic radiation. The laser beam is modulated in conformance with the image information. The modulated beam is reflected through a lens onto a scanning element, typically a rotating polygon having mirrored facets. Many machines use one ROS for each color being printed, the ROS exposing the photoreceptor to light in a pattern representing an image to be printed, as is known in the art. In multipass machines, a single ROS can write the image for each color. The pattern on the exposed photoreceptor is then used to deposit toner on a substrate, which toner is then fused onto the substrate to produce the final printed image.
As an example of the environment in which embodiments can be employed, FIG. 1 schematically illustrates an electrophotographic printing machine 1 that uses raster scanners (RIS 128 and ROS 130) and generally employs a photoconductive belt 12. Preferably, the photoconductive belt 12 is made from a photoconductive material coated on a ground layer, which, in turn, is coated on an anti-curl backing layer. Belt 12 moves in the direction of arrow 18 to advance successive portions sequentially through the various processing stations disposed about the path of movement thereof. Belt 12 is entrained about stripping roller 14, tensioning roller 15 and drive roller 16. As roller 16 rotates, it advances belt 12 in the direction of arrow 13.
Initially, a portion of the photoconductive surface passes through charging station A. At charging station A, a corona generating device indicated generally by the reference numeral 122 charges the photoconductive belt 12 to a relatively high, substantially uniform potential.
At an exposure station, B, a controller or electronic subsystem (ESS), indicated generally by reference numeral 129, receives the image signals representing the desired output image and processes these signals to convert them to a continuous tone or greyscale rendition of the image which is transmitted to a modulated output generator, for example the raster output scanner (ROS), indicated generally by reference numeral 130. Preferably, ESS 129 is a self-contained, dedicated minicomputer. The image signals transmitted to ESS 129 may originate from a RIS as described above or from a computer, thereby enabling the electrophotographic printing machine to serve as a remotely located printer for one or more computers. Alternatively, the printer may serve as a dedicated printer for a high-speed computer. The signals from ESS 129, corresponding to the continuous tone image desired to be reproduced by the printing machine, are transmitted to ROS 130. ROS 130 includes a laser with rotating polygon mirror blocks. The ROS will expose the photoconductive belt to record an electrostatic latent image thereon corresponding to the continuous tone image received from ESS 129. As an alternative, ROS 130 may employ a linear array of light emitting diodes (LEDs) arranged to illuminate the charged portion of photoconductive belt 12 on a raster-by-raster basis.
After the electrostatic latent image has been recorded on photoconductive surface, belt 12 advances the latent image to a development station, C, where toner, in the form of liquid or dry particles, is electrostatically attracted to the latent image using commonly known techniques. The latent image attracts toner particles from the carrier granules forming a toner powder image thereon. As successive electrostatic latent images are developed, toner particles are depleted from the developer material. A toner particle dispenser, indicated generally by the reference numeral 144, dispenses toner particles into developer housing 146 of developer unit 138.
With continued reference to FIG. 1, after the electrostatic latent image is developed, the toner powder image present on belt 12 advances to transfer station D. A print sheet 148 is advanced to the transfer station, D, by a sheet feeding apparatus, 150. Preferably, sheet feeding apparatus 150 includes a nudger roll 151 which feeds the uppermost sheet of stack 154 to nip 155 formed by feed roll 152 and retard roll 153. Feed roll 152 rotates to advance the sheet from stack 154 into vertical transport 156. Vertical transport 156 directs the advancing sheet 148 of support material into the registration transport 120 of the invention herein, described in detail below, past image transfer station D to receive an image from photoreceptor belt 12 in a timed sequence so that the toner powder image formed thereon contacts the advancing sheet 148 at transfer station D. Transfer station D includes a corona generating device 158 which sprays ions onto the back side of sheet 148. This attracts the toner powder image from photoconductive surface to sheet 148. The sheet is then detacked from the photoreceptor by corona generating device 159 which sprays oppositely charged ions onto the back side of sheet 148 to assist in removing the sheet from the photoreceptor. After transfer, sheet 148 continues to move in the direction of arrow 60 by way of belt transport 162 which advances sheet 148 to fusing station F.
Fusing station F includes a fuser assembly indicated generally by the reference numeral 170 which permanently affixes the transferred toner powder image to the copy sheet. Preferably, fuser assembly 170 includes a heated fuser roller 172 and a pressure roller 174 with the powder image on the copy sheet contacting fuser roller 172. The pressure roller is cammed against the fuser roller to provide the necessary pressure to fix the toner powder image to the copy sheet. The fuser roll is internally heated by a quartz lamp (not shown). Release agent, stored in a reservoir (not shown), is pumped to a metering roll (not shown). A trim blade (not shown) trims off the excess release agent. The release agent transfers to a donor roll (not shown) and then to the fuser roll 172.
The sheet then passes through fuser 170 where the image is permanently fixed or fused to the sheet. After passing through fuser 170, a gate 180 either allows the sheet to move directly via output 184 to a finisher or stacker, or deflects the sheet into the duplex path 100, specifically, first into single sheet inverter 182 here. That is, if the sheet is either a simplex sheet, or a completed duplex sheet having both side one and side two images formed thereon, the sheet will be conveyed via gate 180 directly to output 184. However, if the sheet is being duplexed and is then only printed with a side one image, the gate 180 will be positioned to deflect that sheet into the inverter 182 and into the duplex loop path 100, where that sheet will be inverted and then fed to acceleration nip 102 and belt transports 110, for recirculation back through transfer station D and fuser 170 for receiving and permanently fixing the side two image to the backside of that duplex sheet, before it exits via exit path 184.
After the print sheet is separated from photoconductive surface of belt 12, the residual toner/developer and paper fiber particles adhering to photoconductive surface are removed therefrom at cleaning station E. Cleaning station E includes a rotatably mounted fibrous brush in contact with photoconductive surface to disturb and remove paper fibers and a cleaning blade to remove the non-transferred toner particles. The blade may be configured in either a wiper or doctor position depending on the application. Subsequent to cleaning, a discharge lamp (not shown) floods photoconductive surface with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof for the next successive imaging cycle.
The various machine functions are regulated by controller 129. The controller is preferably a programmable microprocessor which controls all of the machine functions hereinbefore described. The controller provides a comparison count of the copy sheets, the number of documents being recirculated, the number of copy sheets selected by the operator, time delays, jam corrections, etc. The control of all of the exemplary systems heretofore described may be accomplished by conventional control switch inputs from the printing machine consoles selected by the operator. Conventional sheet path sensors or switches may be utilized to keep track of the position of the document and the copy sheets.
To reduce cost in raster scanner optics, many manufacturers have turned to plastic lenses. In addition to lower cost, plastic lenses can easily be manufactured to include their own holders in the part design. This reduces material costs, manufacturing costs, and assembly costs by part count reduction. It also reduces the part weight. However, raster scanners require an aperture to prevent excess light from passing through the lens. Such apertures typically include a piece of sheet metal with a hole of the right shape and size in it. The area surrounding the lens is therefore covered up and no light can go past the lens except the desired light that goes through the hole. The requirement for such an aperture prevents further cost reduction and part number reduction.
Additional cost and part number reductions can be achieved by including the aperture in the design of the lens. Since the lens is clear, the material to be used for the part must be clear. Thus, an aperture can be formed by surrounding the lens with one or more refractive surfaces that direct the undesired part of the light beam away from the optical path, which can include another lens or a mirror. The excess light can, for example, be absorbed by the housing of the raster scanner.